The goal of this proposal is to determine the role of the hypothalamus in regulating heart rate, arterial pressure, cardiac output and regional circulation. L-glutamate will be used to activate specific hypothalamic sites while arterial pressure and heart rate are monitored. Tritiated L-glutamate will be mixed with the L-glutamate. The site and approximate spread of these microinjections will be labelled by the radioactive L-glutamate when the brains are subsequently processed histologically for autoradiography. These hypothalamic sites will then be correlated to arterial pressure and heart rate changes observed during chemical stimulation. The mechanism for any circulatory changes observed with stimulation will also be evaluated. The parasympathetic or sympathetic mediation of heart rate changes will be determined using selective pharmacological blockade with atropine methyl nitrate and/or timolol. The arterial pressure changes will be analyzed with the radiolabeled microsphere technique to determine the contribution of total peripheral resistance and cardiac output. The peripheral resistance will be further analyzed by the microsphere technique to reveal any specific changes in regional circulations with hypothalamic stimulation.